DESCRIPTION Understanding myo-inositol homeostasis in neurons is important in determining the pathogenesis of numerous neuropsychiatric diseases. NT2-N human neuronal cells show a large increase in inositol concentration compared to undifferentiated precursors. The focus of this proposal is to study the changes in inositol homeostasis, specifically inositol uptake, following neuronal differentiation. Specific Aim #1: To determine the mechanisms by which neurons attain a high inositol concentration. Inositol concentration in neurons (NT2-N) and precursors (NT2) will be compared by as chromatography. Differences in inositol uptake, efflux, de novo synthesis, and consequent lipid incorporation will be evaluated by biochemical assay. Specific Aim #2: To characterize the expression and regulation of inositol uptake proteins following neuronal differentiation. Differences in transcription and translation of the sodium/myo-inositol transporter (SMIT) will be quantified by northern and western blot, respectively. Changes in SMIT distribution will also be evaluated by immunocytochemistry. In addition, the regulation of inositol uptake by hormonal receptors and downstream signaling molecules, such as protein kinases, will be investigated.